I felt the same way when I rented a K-5 as a K-x user. I was expecting to look at my photos and say "Wow!" but I didn't. About a year after that I bought a K-5 and eventually grew to love it.
I'm thinking my initial response was due to a couple of things. One was differences in controls, so that when shooting in the heat of the moment, I might not be able to adjust the setting I want quickly and may not have had it set in the best way. The other was that I was just running my images through the same process as the K-x, and the K-5 needed slightly different tweaks.
Now I have a K-3 and have felt some of the same feelings when reviewing my photos. I had a couple of high ISO shots early on that seemed very noisy compared to what I was expecting. As I have had it for a few weeks now, I find I need to sharpen less on the K-3 and that helps the noise issue quite a bit.
So if you just apply the exact same preset to a photo that would have worked well for a K-5 image, it may not work as well with a K-3 image. I'm still experimenting with processing, NR, WB, and everything else for the K-3 and am finding the old bag of tricks doesn't always work now. I need some new tricks or to revise some old ones I think.
That being said I have taken some images with the K-3 that I'm quite happy with so my initial buyer's remorse has lessened quite a bit. I'm hopeful I'll continue to get used to it and how to process the images as well as some firmware/software updates to accommodate it that are surely on the way.
FYI, I always shoot RAW so these comments are all based on that.
Here's a photo from Sunday that I like. Taken with the K-3 and DA 18-135 (not my best lens, but probably the best to haul with me skiing)
Processed in LR4. Light wasn't great, but not terrible. Detail came out well I thought.